Thursday, 25 February 2016

LGPG111 Generator Protection Relay

Protection of generatorsElectrical protection is
required to quickly detect and initiate shutdown for major electrical
faults associated with the generating plant and, less urgently, to
detect abnormal operating conditions which, if sustained, may lead to
plant damage.Abnormal electrical conditions can arise as a result of
some failure with the generating plant itself, but can also be
externally imposed on the generator. Common categories of faults and
abnormal conditions to be electrically detected are listed as follows:
(Not all conditions have to be detected for all applications.)MAJOR ELECTRICAL FAULTS* Insulation failure of stator windings or connectionsSECONDARY ELECTRICAL FAULTS· Insulation failure of excitation system· Failure of excitation system· Unsynchronised over voltageABNORMAL PRIME MOVER OR CONTROL CONDITIONS· Failure of prime mover· Over frequency· Over fluxing· Dead machine energisation· Breaker FlashoverSYSTEM RELATED· Feeding an uncleared fault· Prolonged or heavy unbalanced loading· Prolonged or heavy overload· Loss of synchronism· Over frequency· Under frequency· Synchronised over voltage· Over fluxing· Under voltageIn addition to the range of
electrical protection required for a generator, varying types and levels
of mechanical protection are necessary, such as vibration detection,
lubricant and coolant monitoring, etc.The action required following response of an element of electrical or mechanicalprotection is often categorised as follows:· Urgent shutdown· Non-urgent shutdown· Alarm only

An
urgent shutdown would be required, for example, if a phase to phase
fault occurred within the generator electrical connections. A non-urgent
shutdown might be sequential, where the prime mover may be shutdown
prior to electrically unloading the generator, in order to avoid over
speed in the case of a steam turbine. A nonurgent shutdown may be
initiated in the case of continued unbalanced loading. In the event of
unbalanced loading, it is desirable that an alarm should be given before
shutdown becomes necessary, in order to allow for possible operator
intervention to remedy the situation.For urgent tripping, it may be
desirable to electrically maintain the shutdown condition with latching
protection output contacts, which would require manual resetting. For a
non-urgent shutdown, it may be required that the output contacts reset
without intervention, so that production of power can be recommenced as
soon as possible. LGPG111 integrated protectionThe
LGPG111 incorporates the commonly required protection functions for a
wide variety of generating plant applications in a single integrated
package, see Figure . Flexible scheme logic is also provided to allow
the protection output contacts of the package to be configured to
execute required categories of action. Optically-isolated logic inputs
are provided to allow the status of external plant to be monitored and
to exercise control over the protection functions. It is also possible
for mechanical protection functions to initiate alarms or action via the
LGPG111 scheme logic and to be monitored via the serial communications
facility provided with the protection package.

With its frequency
tracking system, the LGPG111 is able to maintain all protection
functions in service over a wide range of operating frequency. It should
not be necessary, for instance, to disable the negative phase sequence
thermal protection when running a generator at low frequency; as might
be necessary with existing discrete relay schemes. This LGPG111
capability will be of especial interest for pumped storage generation
schemes, where synchronous machines would be operated from a variable
frequency supply when in pumping mode. Additionally, in the case of
combined cycle generating plant, it may be necessary to excite and
synchronise a steam turbine generating set with a gas turbine set at low
frequency, prior to running up to nominal frequency and synchronising
with the power system.When LGPG111 protection functions are required
to operate accurately at low frequency, it will be necessary to use
CT’s with larger cores. In effect the CT kneepoint voltage requirements
will be multiplied by fn/f,where f is the minimum required operating
frequency and fn is the nominal operating frequency.In the case of a
synchronous machine at a pumped storage plant being operated in the
motoring mode, it would be necessary to disable reverse power protection
in this mode. This could be accomplished by switching to the LGPG111’s
alternative group of settings where the reverse power protection
function would not be enabled.LGPG111 protection functionsThe following protection functions are provided within the LGPG111 package:· Generator Differential protection (87G)· Stator Earth Fault protection (51N)· Neutral Voltage Displacement protection (59N)· Sensitive Directional Earth Fault protection (67N)· Voltage-Dependent Overcurrent protection (51V)· Negative Phase Sequence Thermal protection (46)· Field Failure protection (40)· Reverse Power protection (32R)· Low Forward Power protection (32L)· Over Voltage protection (59)· Under Voltage protection (27)· Over Frequency protection (810)· Under Frequency protection (81 U)· Voltage Balance protection (60)

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About Sostenes LekuleElectrical Technician and PLCS Programmer. Everyday I`m exploring the world of Electrical to find better solution for Automation. I believe everyday can become a Electrician with the right learning materials. My goal with BLOG is to help you learn Electrical..